Over the years, significant advances have been made in the field of computer graphics. Generally, by utilizing data from an extensive source, in cooperation with various control parameters, dynamic pictures are displayed as to reveal a traversed terrain. Typically, an image generator functions in cooperation with a cathode ray tube display system to provide such dynamic images and visually simulate actual experiences. In one form, such systems have been widely used in simulators for visually training pilots or other operators.
Utilizing one technique, computer image generators process elevation and texture data to provide dynamic, perspective graphic images. While systems have been proposed for displaying such images of terrain, a need continues to exist for improved systems providing displays with sharp, well-defined texture and ridge edges somewhat independent of terrain orientation and with reduced data processing. Additionally, it is important to minimize discernable motion artifacts in such displays.
Typically, elevation and planimetric data for use by an image generator to provide a display is available in a rectangular-coordinate format, e.g. a height field. Conventionally, the height field consists of elevation samples arrayed at coordinate points in a rectangular grid aligned with X-Y datum. Each elevation value at a coordinate point manifests the Z height of the terrain or skin at that X-Y position. Generally, a height field is particularly efficient for representing a complex surface because the X-Y position of each height sample or Z value is imputed from the position or sequence of the height value in the array. Accordingly, the number of elements along each axis and the spacing of the elements need be remembered only once for the entire array; only the Z values are actually stored at each coordinate point or array position, saving two-thirds of the storage. Since only one height value is stored for each position in the array, the field is "single-valued" at every position. The implicit surface or skin associated with the height field thus is non-overlapping in Z, an attribute that is useful herein.
Generally, the system of the present invention involves re-sampling the rectangular coordinate height-field data into a radial form with the establishment of azimuth and range values. A skin or terrain representation is accordingly defined in a radial form and is processed to select samples effecting each picture element (pixel) of a selected viewpoint display. The elevation is then computed in eye space for each radial sample using coordinates of both space formats to generate a basic form of the image that is then textured, shaded and scan converted for display.
Re-sampling the height field data into a radial form is performed in the X-Y coordinates. In the disclosed embodiment, filtering accommodates offset between the two coordinate systems. Pixels are processed from the radial data, again with filtering to attain generally improved image characteristics. Appropriate antialiased texturing, shading and scan conversion operations complete the processing to provide effective pixel display data for a perspective dynamic image display.